At my pediatrician, they did most of the exam with me in only underpants. When the nurse brought my mom and me into the room, she told my mom to take everything off of me except my underpants, and my mom always took that literally by undressing me herself, through age 13. For my exams from 14 through 16, she let me undress myself.
Once I was wearing nothing but underpants, I would sit on the exam table until the nurse came back to walk me down the hall to get my height and weight. When she brought me back to the exam room, I again would sit on the exam table until the doctor arrived. I remember one time it was very cold in the room, and my mom saw me shivering, so she let me put a shirt back on. When the doctor arrived, he wasn't happy with that, and immediately took my shirt off again.
As the doctor would proceed with the exam, he was the one to pull down my underpants for me, and only once, when I was 13, completely remove them, so that I was lying totally naked on the exam table for a skin check. But in all my other exams, up through age 16, the doctor merely pulled my underpants down to mid thigh. Though this was sufficient for him and my mom to see everything, I took some comfort in the fact that I could pull them up quickly if someone else walked in to the room.